(1). Field of the Invention
The present invention relates to an image processing apparatus which serves for digital copying machines and facsimile machines and the like, and performs optimum processing according to the properties of an area obtained by scanning an original document for improving the image quality of recorded images.
(2). Description of the Related Art
With an image processing apparatus such as a digital copying machine and a facsimile apparatus and the like, the image quality has been conventionally improved by discriminating screened half tone, continuous tone and a character area included in an original document, respectively, subjecting the screened halftone area to a smoothing processing to suppress a moirxc3xa9, and subjecting the character area to an emphasizing processing to display characters clearly. To improve the image quality, various image discrimination methods have been used.
As a representative image discrimination processing method, there is known a method for dividing an image into respective predetermined blocks and discriminating each area by using a characteristic parameter representing properties of character and screened halftone images.
As the related art for discriminating character and screened halftone areas in each predetermined block by using a characteristic parameter, for example, some are disclosed in Japanese Unexamined Patent Publication No. Hei 5-167842 and Japanese Unexamined Patent Publication No. Hei 5-41796.
With the xe2x80x9cimage processing apparatusxe2x80x9d disclosed in Japanese Unexamined Patent Publication No. Hei 5-167842, the image quality is improved by comparing the maximum density difference in a predetermined area including a target pixel with a fixed threshold to judge the area, and changing over the post-stage processing. It utilizes a fact that when a black letter is seen in a local area, the maximum density difference which is a difference between the maximum density and the minimum density is larger than the continuous tone area.
Moreover, the xe2x80x9ccopying apparatusxe2x80x9d disclosed in Japanese Unexamined Patent Publication No. Hei 5-41796 improves the image quality by extracting a non-background color pixel using an average value in an Nxc3x97N window including a target pixel as a threshold, and judging whether the target pixel is a character area or not by the pattern of the non-background color pixel to change over the post-stage processing. It utilizes a fact that, in the character area, the length of the same value of the data after binary coding becomes long, and designates the maximum density difference, a run length which is the length of the same value of the data and the like as the characteristic information to compare the characteristic information and the fixed threshold, and when the characteristic information is larger sag than the fixed threshold, it is discriminated to be a character area, and in other cases, it is discriminated to be a photograph area and the like.
When a black letter in a predetermined block is a small letter, the density difference may not be detected clearly depending upon the precision of a scanner, and there may be a case where even if it is a character area, the maximum density difference becomes small. Therefore, with the threshold processing method using a fixed threshold, erroneous separation may be caused, which becomes a significant problem.
Furthermore, when an area in which a character is included is binarized and used as a run length to designate the maximum continuous value of the binary coding result as a characteristic value, in general, binary coding is performed by using an average value in a predetermined area. However, due to the average value determined in a local area, even where the density change is small, there is a possibility of being divided into erroneous binary values by the binary coding processing, which has been a problem.
In view of the foregoing problem, it is an object of the present invention to provide an image processing apparatus which discriminates in which area of the character area, the continuous tone area and the screened halftone area each pixel belongs, with respect to an image signal obtained by two-dimensionally scanning an original document in the main scanning direction and in the sub-scanning direction, and performs a processing for improving the image quality to enhance the detection accuracy of, in particular, black letters.
With a view to attaining the above objects, the gist of the present invention is as follows.
The first gist of the present invention is an image processing apparatus which discriminates an area having different properties with respect to an image signal obtained by scanning an original document, and performs adequate processing to each area, wherein said image processing apparatus comprises:
dividing means for dividing the image signal into local blocks having a predetermined size; and
local characteristic value-computing means having:
a binary coding processing section which converts an image signal in a predetermined block including a target pixel into binary code information, from image signals output from the dividing means in an area to be processed;
a threshold processing section which processes characteristic information in the predetermined block with a threshold determined by selectively using each area (dimension) value of binary values from the binary code information output from the binary coding processing section and number of times that the binary code information is changed; and
a judgement processing section which judges whether the target pixel in the predetermined block is a character area or not based on the processing result of the threshold processing section.
The second gist of the present invention is an image processing apparatus which discriminates an area having different properties with respect to an image signal obtained by scanning an original document, and performs adequate processing to each area, wherein said image processing apparatus comprises:
dividing means for dividing the image signal into local blocks having a predetermined size; and
local characteristic value-computing means having:
an edge detection section for detecting an edge in a local block including a target pixel in the local block output from the dividing means;
a binary coding processing section which converts an image signal in a predetermined block including a target pixel into binary code information, from image signals output from the dividing means in an area to be processed; a threshold processing section which processes characteristic information in the predetermined block with a threshold determined by selectively using each area (dimension) value of binary values from the binary code information output from the binary coding processing section and number of times that the binary code information changed; and a judgement processing section which judges whether the target pixel is a character area or not based on the processing result of the threshold processing section; and
a color judgement processing section for judging whether the target pixel which is an edge is a monochrome edge or a color edge, based on the edge detection results of the edge detection section.
The third gist of the present invention is an image processing apparatus which discriminates an area having different properties with respect to an image signal obtained by scanning an original document, and performs adequate processing to each area, wherein said image processing apparatus comprises:
dividing means for dividing the image signal into local blocks having a predetermined size; and
local characteristic value-computing means having:
an edge detection section for detecting an edge in a predetermined block including a target pixel in the predetermined block output from the dividing means;
a binary coding processing section which converts an image signal in a predetermined block including a target pixel into binary code information, from image signals output from the dividing means in an area to be processed; a threshold processing section which processes characteristic information in the predetermined block with a threshold determined by selectively using each area (dimension) value of binary values from the binary code information output from the binary coding processing section and number of times that the binary code information is changed; and a judgement processing section which judges whether the target pixel is a character area or not based on the processing result of the threshold processing section; and
an edge arrangement judging section for judging the edge arrangement in the predetermined block including the target pixel, based on the edge detection result of the edge detection section.
The processing of the image processing apparatus according to the first gist is such that the image signal obtained by scanning the original document is divided into local blocks having a predetermined size by the dividing means, and the image signal in a predetermined block including a target pixel from the image signals in the divided block to be processed is transmitted to a local characteristic value-computing means.
The image signal transmitted to the local characteristic value-computing means is converted into binary code information by the binary coding processing section, and each area value of binary values and number of times that the binary code information is changed are calculated, a threshold of the characteristic information is determined by properly and selectively using each area value and the change count, and in the threshold processing section, the characteristic information in the predetermined block is processed based on the threshold.
Then, based on the threshold processing results of the characteristic information in the predetermined block, the judgement processing section judges whether the image signal of the target pixel in the predetermined block is character information or not.
When the image signal in the predetermined block is discriminated to be a character area by the above described local characteristic value-computing means, a proper processing such as an emphasizing processing and the like is performed for the character area.
Therefore, according to the construction of the first gist, when edges of, for example, black letters are detected by processing the characteristic information in the predetermined block used at the time of detection of black letters and the like with the threshold, it becomes possible to maintain the detection accuracy not only for large letters but also for small letters, which are generally considered to be difficult to be detected, not by using a fixed threshold as a threshold for the threshold processing, but by properly changing over the threshold according to the area of the predetermined area after binary coding and the number of times that the binary values are changed.
In particular, by utilizing a fact that small letters and fine letters have an area (dimension) different from that of large letters in a predetermined block, a binary area after binary coding is used for changing over the threshold. When the area is small, the threshold of the characteristic information is set to be wide, enabling to correspond to small letters and fine letters, thereby the detection accuracy of small letters and fine letters can be increased compared to the detection accuracy when using a fixed threshold of the characteristic information.
Moreover, when, for example, a small letter is close to other letters, it may be judged as a wide area. In that case, however, since the number of times that the binary values are changed is larger than a predetermined number of times, by including such a change count in a parameter for determining the threshold of the characteristic information, letters can be properly detected even if small letters are formed densely.
The processing of the image processing apparatus according to the second gist is such that the image signal obtained by scanning the original document is divided into predetermined local blocks by the dividing means, and the divided image signal is transmitted to a local characteristic value-computing means.
The image signal transmitted to the local characteristic value-computing means is transmitted to an edge detection section and a binary coding processing section.
With respect to the image signal transmitted to the edge detection section, edges in a predetermined block are detected.
The image signal transmitted to the binary coding processing section is converted into binary code information, and each area value of binary values and the number of times that the binary code information is changed are calculated, and a threshold of the characteristic information is determined by selectively using each area value and the change count, and based on the threshold, the threshold processing of the characteristic information in the predetermined block is performed in the threshold processing section. Then, from the threshold processing result of the characteristic information in the predetermined block, it is judged whether the target pixel in the predetermined block is a character area or not by the judgement processing section.
Moreover, the edge in the predetermined block detected by the edge detection section is subjected to color judgement by the color judgement processing section, and it is judged whether the target pixel which is an edge is a monochrome edge or a color edge.
Then, from the results of judgement of the character edge by the judgement processing section and color judgement of the edge by the color judgement processing section, proper processing is performed for each area.
According to the construction of the second gist, therefore, by properly changing over the threshold used for the threshold processing of the characteristic information, depending upon the area after binary coding of the predetermined block and the number of times that the binary values are changed, sufficient detection accuracy can be maintained not only for large letters but also for small letters which are generally considered to be difficult to be detected, as well as differentiation between monochrome letters and color letters becomes possible. Hence, emphasizing processing suitable for the monochrome letters and color letters can be performed properly, thereby an image processing apparatus which can produce a high quality image can be provided.
The processing of the image processing apparatus according to the third gist is such that the image signal obtained by scanning the original document is divided into predetermined local blocks by the dividing means, and the divided image signal including a target pixel in a predetermined area is transmitted to a local characteristic value-computing means.
The image signal transmitted to the local characteristic value-computing means is transmitted to an edge detection section and a binary coding processing section.
With respect to the image signal transmitted to the edge detection section, edges in a predetermined block are detected.
The image signal transmitted to the binary coding processing section is converted into binary code information, and each area value of binary values and the number of times that the binary code information is changed are calculated, and a threshold of the characteristic information is determined by selectively using each area value and the change count, and based on the threshold, the threshold processing of the characteristic information in the predetermined block is performed in the threshold processing section. Then, from the threshold processing result of the characteristic information in the predetermined block, it is judged whether the target pixel in the predetermined block is a character area or not by the judgement processing section.
Moreover, the detected result by the edge detection section, it is judged whether it is an arrangement of the character edge or not by the edge arrangement judging section.
Then, from the results of judgement of the character edge by the judgement processing section and judgement of the edge arrangement by the edge arrangement judging section, proper processing is performed for each area.
According to the construction of the third gist, therefore, by properly changing over the threshold used for the threshold processing of the characteristic information, depending upon the area after binary coding of the predetermined area and the number of times that the binary values are changed, sufficient detection accuracy can be maintained not only for large letters but also for small letters which are generally considered to be difficult to be detected, as well as the character edge can be discriminated based on the edge arrangement. Hence, the character edge can be reliably discriminated.
Since characters can be emphasized in the area where it is judged to be a character area, an image processing apparatus which can produce clear and vivid black letters can be provided.